Hybrid type working machine

ABSTRACT

A charge accumulating circuit accumulates regeneration power. The charge accumulating circuit includes a DC bus line which is connected to a smoothing capacitor, a charge accumulating capacitor with an internal resistance, and a converter which connects the DC bus line and the charge accumulating capacitor to each other, and performs a charge/discharge operation. The control device changes the OFF state of the first switch to the ON state when the start key is turned on, measures a physical quantity involved with a discharge characteristic of the charge accumulating capacitor, and calculates at least one of the internal resistance and a capacitance of the charge accumulating capacitor on the basis of a measurement result.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hybrid type working machine whichconverts kinetic energy or potential energy into electric energy,accumulates electricity in a charge accumulating device, and drives adriving system by using accumulated electric energy.

Priority is claimed on Japanese Patent Application No. 2009-052197 filedMar. 5, 2009 and Japanese Patent Application No. 2009-262062 filed Nov.17, 2009, the content of which is incorporated herein by reference.

2. Description of the Related Art

In recent years, out of consideration for the environment, improvementsin performance, such as fuel savings, lower pollution, and lower noise,have been demanded in power generating machines, such as constructionworking machines. In order to meet the demand, working machines such ashydraulic shovels using an electric motor instead of or to assist ahydraulic pump have been introduced. In a working machine attached withthe electric motor, excessive kinetic energy generated from the electricmotor is converted into electric energy, and accumulated in a capacitoror the like. As the capacitor, for example, an electric double-layercondenser (capacitor) is used.

The capacitor deteriorates over long-term usage due to repeatingcharge/discharge operations, overcharging, overdischarging, or heating.The deterioration state may be determined by measuring the internalresistance of the capacitor (refer to JP-A-2007-155586).

SUMMARY OF THE INVENTION

An object of the invention is to provide a technology of measuring acharacteristic of a capacitor in a hybrid type working machine using thecapacitor.

According to an aspect of the invention, there is provided a hybrid typeworking machine including: a first electric motor which performs a powerrunning operation driven by a supply of electric power and aregenerating operation generating electric power; a first electriccircuit which controls the power running operation and the regeneratingoperation of the first electric motor; a charge accumulating circuitwhich supplies electric power to the first electric motor andaccumulates electric power regenerated by the first electric motor; acontrol device which controls the first electric circuit and the chargeaccumulating circuit; and a start key which activates the controldevice, wherein the charge accumulating circuit includes: a DC bus linewhich is connected to the first electric circuit and in which asmoothing capacitor is connected between a ground line and a power line;a charge accumulating capacitor with an internal resistance; a converterwhich connects the DC bus line and the charge accumulating capacitor toeach other, and performs a discharge operation of supplying electricenergy from the charge accumulating capacitor to the DC bus line and acharge operation of supplying electric energy from the DC bus line tothe charge accumulating capacitor; and a first switch which performsswitching between an ON state and an OFF state, the ON state allowingcurrent to flow between the charge accumulating capacitor and the DC busline, and the OFF state not allowing current to flow between the chargeaccumulating capacitor and the DC bus line, and wherein the controldevice switches the first switch from the OFF state to the ON state dueto the start key being turned on, measures a physical quantity involvedwith a discharge characteristic of the charge accumulating capacitor,and calculates at least one of the internal resistance and a capacitanceof the charge accumulating capacitor on the basis of a measurementresult.

Upon starting the hybrid type working machine, it is possible to measurethe internal resistance of the charge accumulating capacitor.Accordingly, it is possible to determine the deterioration state of thecharge accumulating capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a hybrid type working machine according to afirst example.

FIG. 2 is a block diagram of the hybrid type working machine accordingto the first example.

FIG. 3 is an equivalent circuit diagram of a charge accumulating circuitused in the hybrid type working machine according to the first example.

FIG. 4 is an equivalent circuit diagram for illustrating a method ofmeasuring a characteristic of a capacitor of the hybrid type workingmachine according to the first example.

FIG. 5 is a graph showing an example of a variation in voltage andcurrent for illustrating a method of measuring a characteristic of acapacitor of the hybrid type working machine according to the firstexample.

FIG. 6 is a graph showing an example of a variation in voltage andcurrent for illustrating a method of measuring a characteristic of acapacitor of the hybrid type working machine according to a secondexample.

FIG. 7 is an equivalent circuit diagram for illustrating a method ofmeasuring a characteristic of a capacitor of the hybrid type workingmachine according to a third example.

FIG. 8 is a graph showing an example of a variation in voltage andcurrent for illustrating a method of measuring a characteristic of acapacitor of the hybrid type working machine according to the thirdexample.

FIG. 9 is a graph showing an actual measurement value of a variation involtage and current of a capacitor of the hybrid type working machineaccording to the third example.

FIG. 10 is a graph showing an example of a variation in voltage andcurrent for illustrating a method of measuring a characteristic of acapacitor of the hybrid type working machine according to a fifthexample of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, first and second examples will be described with referenceto the drawings.

FIRST EXAMPLE

FIG. 1 is a side view showing a hybrid type working machine according toa first example. A lower traveling body (base) 1 is mounted with anupper turning body 3 with a turning mechanism 2 therebetween. Theturning mechanism 2 includes an electric motor, and rotates the upperturning body 3 in the clockwise direction or the counter-clockwisedirection. The upper turning body 3 is mounted with a boom 4. The boom 4is adapted to swing with respect to the upper turning body 3 by a boomcylinder 7 which is driven by a hydraulic pressure. The front end of theboom 4 is attached with an arm 5. The arm 5 is adapted to swing in thefront-back direction with respect to the boom 4 by an arm cylinder 8which is driven by a hydraulic pressure. The front end of the arm 5 isattached with a bucket 6. The bucket 6 is adapted to swing with respectto the arm 5 in the vertical direction by a bucket cylinder 9 which isdriven by a hydraulic pressure. The upper turning body 3 is mounted witha cabin 10 which accommodates a driver.

FIG. 2 shows a block diagram of the hybrid type working machine. In FIG.2, a mechanical power system is depicted by the double line, ahigh-pressure hydraulic line is depicted by the bold solid line, anelectric system is depicted by a thin solid line, and a pilot line isdepicted by the dashed line.

A driving shaft of an engine 11 is connected to an input shaft of atransmission 13. As the engine 11, an engine for generating a drivingforce by using fuel other than electricity, for example, an internalcombustion engine such as a diesel engine is used. The engine 11 isnormally driven during the operation of the working machine.

A driving shaft of an electric motor generator 12 is connected toanother input shaft of the transmission 13. The electric motor generator12 is capable of performing both operations, that is, an electric(assist) operation and an electricity generating operation. As the motorgenerator 12, for example, an IPM (interior permanent magnet) motorhaving a magnet embedded inside a rotor is used.

The transmission 13 includes two input shafts and one output shaft. Theoutput shaft is connected to a driving shaft of a main pump 14.

In the case where a load applied to the engine 11 is large, the electricmotor generator 12 performs an assist operation, and the driving forceof the electric motor generator 12 is transmitted to the main pump 14through the transmission 13. Accordingly, a load applied to the engine11 is reduced. On the other hand, in the case where a load applied tothe engine 11 is small, the driving force of the engine 11 istransmitted to the electric motor generator 12 through the transmission13, so that the electricity generating operation of the electric motorgenerator 12 is performed. The selection of the assist operation or theelectricity generating operation of the electric motor generator 12 isperformed by an inverter 18 connected to the electric motor generator12. The inverter 18 is controlled by a control device 30.

The control device 30 includes a CPU (central processing unit) 30A andan internal memory 30B. The CPU 30A executes a driving control programstored in the internal memory 30B. The control device 30 catches thedriver's attention by displaying a deterioration state and the like ofvarious devices on a display device 35.

The main pump 14 supplies a hydraulic pressure to a control valve 17through the high-pressure hydraulic line 16. The control valve 17distributes a hydraulic pressure to hydraulic motors 1A and 1B, the boomcylinder 7, the arm cylinder 8, and the bucket cylinder 9 on the basisof the command from the driver. The hydraulic motors 1A and 1B driveleft and right crawlers provided in the lower traveling body 1 shown inFIG. 1, respectively.

An input/output terminal of the electric system of the electric motorgenerator 12 is connected to a charge accumulating circuit 90 throughthe inverter 18. The inverter 18 performs an operation control of theelectric motor generator 12 on the basis of the command from the controldevice 30. The charge accumulating circuit 90 is connected to a turningelectric motor 21 through another inverter 20. The charge accumulatingcircuit 90 and the inverter 20 are controlled by the control device 30.

During the assist operation of the electric motor generator 12, thedemanded electric power is supplied from the charge accumulating circuit90 to the electric motor generator 12 through the inverter 18. Duringthe electricity generating operation of the electric motor generator 12,the power generated by the electric motor generator 12 is supplied tothe charge accumulating circuit 90 through the inverter 18.

The turning electric motor 21 is driven by alternative current on thebasis of the PWM (pulse width modulation) control signal from theinverter 20, and is capable of performing both operations, that is, apower running operation and a regenerating operation. As the turningelectric motor 21, for example, an IPM motor is used. The IPM motorgenerates a large induced electromotive force during the regeneratingoperation.

During the power running operation of the electric turning motor 21, arotation force of the turning electric motor 21 is transmitted to theturning mechanism 2 shown in FIG. 1 through a transmission 24. At thistime, the transmission 24 decreases the rotation speed. Accordingly, therotation force generated in the turning electric motor 21 is increasedand transmitted to the turning mechanism 2. In addition, during theregenerating operation, the rotation movement of the upper rotation body3 is transmitted to the turning electric motor 21 through thetransmission 24, so that a regenerating power is generated from theturning electric motor 21. At this time, the transmission 24 allows therotation speed to be fast on the contrary to the power runningoperation. Accordingly, it is possible to increase the rotationfrequency of the turning electric motor 21.

The resolver 22 detects the position in the rotation direction of therotation shaft of the turning electric motor 21. The detection result isinput to the control device 30. When the positions in the rotationdirection of the rotation shaft before and after the operation of theturning electric motor 21 are detected, it is possible to obtain theturning angle and the turning direction.

A mechanical brake 23 is connected to the rotation shaft of the turningelectric motor 21, and generates a mechanical braking force. The brakestate or the release state of the mechanical brake 23 is selected by anelectromagnetic switch under the control of the control device 30.

A pilot pump 15 generates a pilot pressure required for the hydraulicoperation system. The generated pilot pressure is supplied to anoperation device 26 through the pilot line 25. The operation device 26includes a lever or a pedal, and is operated by the driver. Theoperation device 26 changes a primary hydraulic pressure supplied fromthe pilot line 25 to a secondary hydraulic pressure in accordance withthe driver's operation. The secondary hydraulic pressure is transmittedto the control valve 17 through the hydraulic line 27, and istransmitted to a pressure sensor 29 through another hydraulic line 28.

The detection result of the pressure detected by the pressure sensor 29is input to the control device 30. Accordingly, the control device 30 iscapable of detecting the operation states of the lower traveling body 1,the turning mechanism 2, the boom 4, the arm 5, and the bucket 6.Particularly, in the hybrid type working machine according to the firstexample, the turning electric motor 21 drives the turning mechanism 2.For this reason, it is preferable to highly precisely detect theoperation amount of the lever for controlling the turning mechanism 2.The control device 30 is capable of highly precisely detecting theoperation amount of the lever through the pressure sensor 29.

When the operator turns on a start key 32, the control device 30 isactivated. The control device 30 starts the control of the engine 11,the inverters 18 and 20, and the charge accumulating circuit 90. Thecontrol device 30 is capable of detecting a state (non-operation state)in which any one of the lower traveling body 1, the turning mechanism 2,the boom 4, the arm 5, and the bucket 6 is not operated, and neither thepower supply to the charge accumulating circuit 90 nor the compulsorypower acquisition from the charge accumulating circuit 90 are performed.

FIG. 3 shows an equivalent circuit diagram of the charge accumulatingcircuit 90. The charge accumulating circuit 90 includes a chargeaccumulating capacitor 19, a converter 100, and a DC bus line 110.

The converter 100 connects the charge accumulating capacitor 19 and theDC bus line 110 to each other. In an electric circuit connecting thecharge accumulating capacitor 19 and the DC bus line 110, a chargingresistor 108 and a first switch 115 are inserted in series to the chargeaccumulating capacitor 19. The charge accumulating capacitor 19 has, forexample, a structure in which a plurality of electric double-layercondensers (capacitors) is connected in series. A capacitance of thecharge accumulating capacitor 19 is denoted by Cc, and an internalresistance is denoted by Rc.

The first switch 115 is controlled by the control device 30, and is usedto select an ON state in which the charge accumulating capacitor 19 isconnected to the DC bus line 110 or an OFF state in which the chargeaccumulating capacitor 19 is not connected to the DC bus line 110. Asecond switch 116 is connected to the charging resistor 108 in parallel.The second switch 116 is controlled by the control switch 30, and iscapable of realizing a short-circuit state between terminals of thecharging resistor 108.

A capacitor voltmeter 106 measures a voltage between terminals of thecharge accumulating capacitor 19, and inputs the measurement result tothe control device 30. The capacitor ammeter 107 measures acharge/discharge current of the charge accumulating capacitor 19, andinputs the measurement result to the control device 30.

A thermometer 112 measures a temperature of the charging resistor 108,and inputs the measurement result to the control device 30. Theresistance value of the charging resistor 108 may change in accordancewith the temperature thereof. The control device 30 calculates theresistance value of the charging resistor 108 at the current time pointon the basis of the rated resistance value, the temperaturecharacteristic, and the temperature at the current time point of thecharging resistor 108.

The DC bus line 110 includes a ground line and a power line. A smoothingcapacitor 105 is connected between the ground line and the power line.The ground line and the power line of the DC bus line 110 arerespectively connected to the electric motor generator 12 and theturning electric motor 21 through the inverters 18 and 20. The voltagebetween the ground line and the power line of the DC bus line 110 ismeasured by a DC bus line voltmeter 111, and the measurement result isinput to the control device 30.

The converter 100 includes a boosting IGBT (insulated gate bipolartransistor) 102A, a voltage-dropping IGBT 102B, and a reactor 101. Theemitter of the boosting IGBT 102A is connected to the ground line of theDC bus line 110, and the collector of the voltage-dropping IGBT 102B isconnected to the power line of the DC bus line 110. The collector of theboosting IGBT 102A is connected to the emitter of the voltage-droppingIGBT 102B. The diodes 102 a and 102 b are respectively connected to theboosting IGBT 102A and the voltage-dropping IGBT 102B in parallel insuch a manner that the direction from the emitter to the collector is aforward direction.

The interconnection point between the boosting IGBT 102A and thevoltage-dropping IGBT 102B is connected to one terminal of the chargeaccumulating capacitor 19 through the reactor 101, and the ground lineof the DC bus line 110 is connected to the other terminal of the chargeaccumulating capacitor 19. A third switch 117 is connected in parallelto the reactor 101. The third switch 117 is controlled by the controldevice 30 so as to be opened or closed. When the third switch 117 isclosed, the terminals of the reactor 101 become in a short-circuitstate.

The control device 30 applies a control PWM (pulse width modulation)voltage to the gate electrodes of the boosting IGBT 102A and thevoltage-dropping IGBT 102B.

Hereinafter, a boosting operation (discharge operation) will bedescribed. The PWM voltage is applied to the gate electrode of theboosting IGBT 102A. When the boosting IGBT 102A is changed from the ONstate to the OFF state, an induced electromotive force is generated inthe reactor 101 in a direction in which a current flows to the collectorof the boosting IGBT 102A. The induced electromotive force is applied tothe DC bus line 110 through the diode 102 b. Accordingly, the DC busline 110 is boosted.

Next, a voltage-dropping operation (charge operation) will be described.The PWM voltage is applied to the gate electrode of the voltage-droppingIGBT 102B. When the voltage-dropping IGBT 102B is changed from the ONstate to the OFF state, an induced electromotive force is generated inthe reactor 101 in a direction in which a current flows from the emitterof the voltage-dropping IGBT 102B to the charge accumulating capacitor19. The charge accumulating capacitor 19 is charged by the inducedelectromotive force. In addition, in the specification, a current in adirection of discharging the charge accumulating capacitor 19 is definedto be positive, and a current in a direction of charging the chargeaccumulating capacitor 19 is defined to be negative.

By referring to FIGS. 4 and 5, a method will be described which measuresthe internal resistance Rc and the capacitance Cc of the chargeaccumulating capacitor 19. This measurement is performed upon startingthe hybrid type working machine. Upon starting the working machine, acharge is accumulated in the charge accumulating capacitor 19 shown inFIG. 3, and a charge is not accumulated in the smoothing capacitor 105.

When the hybrid type working machine is started, the control device 30closes the third switch 117 so as to cause short circuit between theterminals of the reactor 101. The IGBTs 102A and 102B are in an OFFstate. In addition, an induced voltage is not generated yet by theelectric motor generator 12.

FIG. 4 shows an equivalent circuit diagram in the state where theterminals of the reactor 101 are in a short-circuit state. In addition,the forward resistance of the diode 102 b shown in FIG. 3 is assumed tobe 0, and the reverse resistance of the diode 102 a is assumed to beinfinite. The discharge current of the charge accumulating capacitor 19is denoted by i(t). The resistance value of the charging resistor 108 isdenoted by Rr, and the capacitance of the smoothing capacitor 105 isdenoted by Cd.

FIG. 5 shows a discharge characteristic after the timing t=0 of thecharge accumulating capacitor 19 connected to the charging resistor 108and the smoothing capacitor 105 shown in FIG. 4, and specifically showschanges in time of a current i(t), a voltage Vc(t) between terminals ofthe charge accumulating capacitor 19, and a voltage Vd(t) betweenterminals of the smoothing capacitor 105. When the start key 32 (FIG. 2)is turned on, the control device 30 closes the first switch 115 at thetiming t=0. Before the first switch 115 is closed (the timing beforestarting the working machine, and specifically before turning on thestart key 32), a voltage between terminals of the charge accumulatingcapacitor 19 is denoted by V₀. At the time when the first switch 115 isclosed, the current i(t) rises up. At this time, since a voltage drop isgenerated by the internal resistance Rc, the voltage Vc(t) between theterminals of the charge accumulating capacitor 19 drops down.

The smoothing capacitor 105 is charged by the discharge current i(t),and the voltage Vd(t) between the terminals gradually increases. Thedischarge current i(t) gradually decreases in accordance with anincrease in the voltage Vd(t) between the terminals. Since the voltagedrop due to the internal resistance Rc becomes small in accordance witha decrease in the discharge current i(t), the voltage Vc(t) between theterminals of the charge accumulating capacitor 19 gradually increases.When the voltage Vc(t) between the terminals of the charge accumulatingcapacitor 19 becomes equal to the voltage Vd(t) between the terminals ofthe smoothing capacitor 105, the discharge current i(t) becomes 0.

When the discharge current i(t) becomes 0, the voltage Vc(t) between theterminals of the charge accumulating capacitor 19 is lower than thevoltage V₀ between the terminals immediately before the timing t=0.However, since the capacitance Cc of the charge accumulating capacitor19 is sufficiently large compared with the capacitance Cd of thesmoothing capacitor 105, a decrease amount of the voltage Vc(t) betweenthe terminals of the charge accumulating capacitor 19 is extremelysmall.

The current i(t) is expressed by the following expression.

[Expression  1] $\begin{matrix}{{i(t)} = {\frac{V_{0}}{R}{\exp\left( {- \frac{t}{CR}} \right)}}} & \left( {1a} \right) \\{R = {{Rc} + {Rr}}} & \left( {1b} \right) \\{\frac{1}{C} = {\frac{1}{Cc} + \frac{1}{Cd}}} & \left( {1c} \right)\end{matrix}$

In the expressions (1a) to (1c), the following expression is obtainedwhen t=+0.

[Expression  2] $\begin{matrix}{{Rc} = {\frac{V_{0}}{i\left( {+ 0} \right)} - {Rr}}} & (2)\end{matrix}$

The current i(+0) has a magnitude of a current immediately after thefirst switch 115 is closed in response to the starting operation (indetail, a key ON) of the working machine, and may be measured by thecapacitor ammeter 107. The voltage V₀ between the terminals of thecharge accumulating capacitor 19 immediately before closing the firstswitch 115 may be measured by the capacitor voltmeter 106. The magnitudeRr of the charging resistor 108 is already known. Accordingly, it ispossible to calculate the internal resistance Rc from the measurementvalues V₀ and i(+0), and the already known resistance value Rr.

In the case where a variation in the resistance value Rr of the chargingresistor 108 is large due to a temperature variation, it is desirable tocorrect the resistance value of the charging resistor 108 on the basisof the temperature measured by the thermometer 112 shown in FIG. 3.

The following expression is obtained from the expression (1a).

[Expression  3] $\begin{matrix}{C = \frac{\frac{t}{R}}{{\ln\left( \frac{V_{0}}{R} \right)} - {\ln\;{i(t)}}}} & (3)\end{matrix}$

The current i(T₁) at the time point of the timing t=T₁ is measured bythe capacitor ammeter 107. The combined capacitance C is obtained by thefollowing expression.

[Expression  4] $\begin{matrix}{C = \frac{\frac{T_{1}}{R}}{{\ln\left( \frac{V_{0}}{R} \right)} - {\ln\;{i\left( T_{1} \right)}}}} & (4)\end{matrix}$

The capacitance Cd of the smoothing capacitor 105 is already known.

Accordingly, it is possible to calculate the capacitance Cc of thecharge accumulating capacitor 19 from the elapsed time T₁, themeasurement values V₀ and i(T₁), the calculation value of the internalresistance Rc, and the expressions (4), (1b), and (1c).

When the calculation of the internal resistance Rc and the capacitanceCc of the charge accumulating capacitor 19 is completed, the controldevice 30 opens the third switch 117 shown in FIG. 3. Accordingly, it ispossible to perform the charge/discharge operation of the chargeaccumulating capacitor 19.

SECOND EXAMPLE

Next, a method of measuring a characteristic of the capacitor accordingto a second example will be described with reference to FIGS. 4 and 6.

FIG. 6 shows a discharge characteristic after the timing t=0 of thecharge accumulating capacitor 19 connected to the charging resistor 108,the second switch 116, and the smoothing capacitor 105.

At the timing t=0, the sequence of closing the first switch 115 is thesame as that of the first example. In the second example, at the timingt=T₂ before the time point at which i=0, the second switch 116 isclosed. When the second switch 116 is closed, since the DC resistance ofthe closed circuit where the discharge current i(t) flows decreases, thecurrent i(t) rises up. When the current i(t) rises up, the voltage dropgenerated in the internal resistance Rc becomes large, and hence thevoltage Vc(t) between the terminals of the charge accumulating capacitor19 drops down.

The time constant of the closed circuit where the discharge current i(t)flows becomes short due to the short-circuit state of the chargingresistor 108. For this reason, after the timing t=T₂, the current i(t)gradually decreases at a rate characterized by the shorter timeconstant. Since the voltage drop generated in the internal resistance Rcgradually decreases due to a decrease in the current i(t), the voltageVc(t) between the terminals of the charge accumulating capacitor 19gradually increases after the timing t=T₂. The voltage Vd(t) between theterminals of the smoothing capacitor 105 gradually increases at a ratecharacterized by the shorter time constant.

The voltage drop Vr(T₂−0) immediately before the timing t=T₂ by theinternal resistance Rc and the charging resistance Rr is expressed bythe following expression.[Expression 5]Vr(T ₂−0)=i(T ₂−0)×(Rc+Rr)  (5)

The voltage drop Vr(T₂+0) due to the internal resistance Rc immediatelyafter the timing t=T₂ is expressed by the following expression.[Expression 6]Vr(T ₂+0)=i(T ₂+0)×Rc  (6)

Since the voltage across both ends of the capacitance Cc of the chargeaccumulating capacitor 19 and the voltage Vd(t) between the terminals ofthe smoothing capacitor 105 do not discontinuously change, theexpression of Vr(T₂−0)=Vr(T₂+0) is satisfied. Accordingly, the followingexpression is satisfied.[Expression 7]i(T ₂−0)×(Rc+Rr)=i(T ₂+0)×Rc  (7)

In addition, the following expression is satisfied immediately beforethe timing t=T₂.[Expression 8]i(T ₂−0)×Rr=Vc(T ₂−0)−Vd(T ₂−0)  (8)

When the resistance value Rr of the charging resistor 108 is removedfrom the expressions (7) and (8), the following expression is obtained.

[Expression  9] $\begin{matrix}{{Rc} = \frac{{{Vc}\left( {T_{2} - 0} \right)} - {{Vd}\left( {T_{2} - 0} \right)}}{{i\left( {T_{2} + 0} \right)} - {i\left( {T_{2} - 0} \right)}}} & (9)\end{matrix}$

The right-hand member Vc(T₂−0) of the expression (9) may be measured bythe capacitor voltmeter 106, and the Vd(T₂−0) may be measured by the DCbus line voltmeter 111. The current values i(T₂+0) and i(T₂−0) may bemeasured by the capacitor ammeter 107. Accordingly, it is possible tocalculate the internal resistance Rc of the charge accumulatingcapacitor 19 as the left-hand member of the expression (9) from thesemeasurement results. Since the expression (9) does not include theresistance value Rr of the charging resistor 108, it is possible toobtain the internal resistance Rc without the influence of a variationin the resistance value Rr of the charging resistor 108.

The time constant of a decrease in the current i(t) after the timingt=T₂ is C×Rc. Since the internal resistance Rc is calculated on thebasis of the expression (9), when the time constant of a decrease in thecurrent i(t) is known, it is possible to calculate the capacitance Cc ofthe charge accumulating capacitor 19.

It is possible to obtain the time constant of a decrease in the currenti(t) from a variation in the current i(t) after the timing t=T₂ of FIG.6. As an example, it is possible to obtain the time constant from avalue of the current i(t) of at least two points after the timing t=T₂.

When the calculation of the internal resistance Rc and the capacitanceCc of the charge accumulating capacitor 19 is completed, the controldevice 30 opens the second switch 116 and the third switch 117 shown inFIG. 3. Accordingly, it is possible to perform the charge/dischargeoperation of the charge accumulating capacitor 19.

THIRD EXAMPLE

Next, a method of measuring a characteristic of the capacitor accordingto a third example will be described with reference to FIGS. 7 and 8.

FIG. 7 shows an equivalent circuit diagram applied to the third example.Upon starting the hybrid type working machine, a charge is accumulatedin the charge accumulating capacitor 19, and a charge is hardlyaccumulated in the smoothing capacitor 105. When the hybrid type workingmachine is started, the control device 30 (FIGS. 2 and 3) closes thefirst switch 115. Hereinafter, in FIG. 7, it is supposed that the firstswitch 115 is turned on at the timing t=0.

FIG. 8 shows a discharge characteristic of the charge accumulatingcapacitor 19 connected to the charging resistor 108, the reactor 101,and the smoothing capacitor 105 shown in FIG. 7 after the timing t=0.When the first switch 115 becomes an ON state at the timing t=0 byturning on the start key 32 (FIG. 2), the discharge current i(t) of thecharge accumulating capacitor 19 starts to flow. However, the timingindicating the maximum value of the discharge current i(t) is slightlylater than the timing t=0 due to the influence of the reactor 101. Afterthe discharge current i(t) becomes maximal, the discharge current i(t)gradually decreases, and becomes 0 at the time point when the voltagebetween the terminals of the charge accumulating capacitor 19 is equalto the voltage between the terminals of the smoothing capacitor 105. Ingeneral, when the combined resistance, the inductance, and the combinedcapacitance of the LCR circuit shown in FIG. 7 are respectively denotedby R, L, and C, the expression of R²>(4 L/C) is satisfied. For thisreason, overdamping occurs instead of vibration damping.

Before the first switch 115 becomes an ON state, the voltage Vc(t)measured by the capacitor voltmeter 106 is denoted by V₀. When thedischarge current i(t) flows by turning on the first switch 115, thevoltage Vc(t) between the terminals decreases due to the voltage dropcaused by the internal resistance Rc of the charge accumulatingcapacitor 19. As the discharge current i(t) decreases, the voltage Vc(t)increases. However, since a part of the charge has moved from the chargeaccumulating capacitor 19 to the smoothing capacitor 105 before thedischarge current i(t) is 0, the voltage Vc(t) is not recovered to theinitial value V₀. In detail, the expression of ΔV=V₀−Vc(∞)=V₀×Cd/(Cc+Cd)is satisfied. Here, Cd denotes the capacitance of the smoothingcapacitor 105.

The voltage Vc(t) measured by the voltmeter 106 shown in FIG. 7 isexpressed by the following expression.

[Expression  10] $\begin{matrix}{{{Vc}(t)} = {V_{0} - {\frac{1}{Cc}{\int_{0}^{t}{{i(t)}\ {\mathbb{d}t}}}} - {{Rc} \cdot {i(t)}}}} & (10)\end{matrix}$

When t=T₃ by modifying the expression (10), the following expression isobtained.

[Expression  11] $\begin{matrix}{{Cc} = {\frac{1}{V_{0} - {{Vc}\left( T_{3} \right)} - {{Rc} \cdot {i\left( T_{3} \right)}}}{\int_{0}^{T_{3}}{{i(t)}\ {\mathbb{d}t}}}}} & (11)\end{matrix}$

When the period from the timing t=0 to the timing T₃ is set to besufficiently long until the discharge current i(t) is almost equal to 0as shown in FIG. 8, Rc·i(T₃) of the expression (11) may be approximateto 0. When the elapsed time t is set to be large, V₀−Vc(t) isapproximate to the finite value ΔV, and does not become 0. In the casewhere Rc·i(T₃) is sufficiently small compared with V₀−Vc(T₃), theexpression (11) is approximate as below.

[Expression  12] $\begin{matrix}{{Cc} \approx {\frac{1}{V_{0} - {{Vc}\left( T_{3} \right)}}{\int_{0}^{T_{3}}{{i(t)}\ {\mathbb{d}t}}}}} & (12)\end{matrix}$

It is possible to measure the voltage Vc(T₃) at the timing t=T₃. It ispossible to calculate the right-hand integral term by measuring thedischarge current i(t) from the timing t=0 to the timing t=T₃ at theshort time interval capable of tracing a variation in current.Accordingly, it is possible to calculate the capacitance Cc of thecharge accumulating capacitor 19 from the expression (12).

As an example, when Rc·i(T₃) is equal to or less than 1/10 of V₀−Vc(T₃)in the expression (11), the approximation of the expression (12) issatisfied at sufficient precision. Since the voltage decrease amount ΔVshown in FIG. 8 is smaller than V₀−Vc(T₃), it is supposed that theapproximation of the expression (12) may be applied when Rc·i(T₃) isequal to or less than 1/10 of ΔV.

The voltage decrease amount ΔV at the timing t=∞ is V₀×Cd/(Cc+Cd). Thatis, the time when Rc·i(T₃) is equal to or less than 1/10 ofΔV=V₀×Cd/(Cc+Cd) may be adopted as the time T₃. At this time, as thecapacitance Cc and the internal resistance Rc of the charge accumulatingcapacitor 19, the precise value at the current time point may not beused, but the initial value or the rated value of the capacitance Cc andthe internal resistance Rc of the charge accumulating capacitor 19 maybe used.

In addition, in the state where the charge accumulating capacitor 19 isnot degraded, the discharge current i(t) shown in FIG. 8 may bemeasured, and the timing T₃ at which Rc·i(t) is equal to or less than1/10 of ΔV=V₀×Cd/(Cc+Cd) may be determined in advance. As the timing T₃used in measuring the characteristic of the capacitor at the time ofstartup of the hybrid type working machine, the timing T₃ which isdetermined in advance in the state where the charge accumulatingcapacitor is not degraded may be adopted.

When t=T₄ by modifying the expression (11), the following expression isobtained.

[Expression  13] $\begin{matrix}{{Rc} = \frac{V_{0} - {{Vc}\left( T_{4} \right)} - {\frac{1}{Cc}{\int_{o}^{T_{4}}{{i(t)}\ {\mathbb{d}t}}}}}{i\left( T_{4} \right)}} & (13)\end{matrix}$

It is possible to measure the voltage Vc(T₄) and the current i(T₄) ofthe expression (13). It is possible to calculate the right-hand integralterm by measuring the discharge current i(t) from the timing t=0 to thetiming t=T₄ at the short time interval capable of tracing a variation incurrent. The capacitance Cc is calculated by using the expression (12).Accordingly, it is possible to calculate the internal resistance Rc fromthe expression (13).

When the denominator i(T₄) of the expression (13) is 0, the calculationerror occurs. Accordingly, as shown in FIG. 8, it is necessary to selectthe timing T₄ in a period during which the discharge current i(T₄) isnot 0. In detail, it is necessary to select the timing T₄ to be earlierthan the timing T₃. In addition, when the timing T₄ is selected so as tobe earlier than the timing at which the discharge current i(t) has themaximum value, the measurement error of the integral term of theexpression (13) becomes large. For this reason, it is desirable toselect the timing T₄ to be later than the timing at which the dischargecurrent i(t) has the maximum value.

When the current i(T₄) is substantially equal to 0, the measurementerror of the current i(T₄) has a large influence on the calculationresult of the internal resistance Rc. For this reason, it is desirableto select the timing T₄ under the condition that the current i(T₄) issufficiently large. As an example, it is desirable to select the timingT₄ under the condition that the current i(T₄) is equal to or larger than⅓ of the maximum value of the discharge current i(t).

FIG. 9 shows an example of the actual measurement result of the voltageVc(t) between the terminals of the charge accumulating capacitor 19 andthe discharge current i(t). The horizontal axis indicates the elapsedtime having the unit of “second” from the ON state of the first switch115. The left vertical axis indicates the voltage Vc(t) between theterminals at an arbitrary unit. The right vertical axis indicates thedischarge current at an arbitrary unit.

At the timing 0, the discharge current i(t) abruptly rises up. Byintegrating the discharge current i(t), it is possible to calculate theintegral terms of the expressions (12) and (13).

In the third example, as shown in the expressions (12) and (13), it isnot necessary to use the capacitance of the smoothing capacitor 105 andthe resistance value of the charging resistor 108 for the calculation ofthe capacitive characteristic of the charge accumulating capacitor 19.For this reason, it is possible to measure the characteristic of thecharge accumulating capacitor 19 without the influence of the elements.In addition, it is not necessary to short-circuit the both ends of thereactor 101.

FOURTH EXAMPLE

Next, a fourth example will be described. In the fourth example, theinternal resistance Rc is calculated by approximating the third term inthe numerator of the right-hand side of the expression (13) to 0. Thatis, the internal resistance Rc is calculated by the followingexpression.

[Expression  14] $\begin{matrix}{{Rc} = \frac{V_{0} - {{Vc}\left( T_{4} \right)}}{i\left( T_{4} \right)}} & (14)\end{matrix}$

The third term in the numerator of the right-hand side of the expression(13) is a decrease amount of the voltage corresponding to the chargeamount vanished by the discharge of the charge accumulating capacitor 19until the timing T₄. The decrease amount of the voltage is smaller thanthe decrease amount of the voltage ΔV=V₀×Cd/(Cc+Cd) when the elapsedtime t is ∞. Accordingly, when the timing T₄ is selected so thatV₀−Vc(T₄) is sufficiently larger than ΔV, the expression (14) isobtained with high precision. As an example, when the timing T₄ isselected so that V₀−Vc(T₄) is equal to or larger than five times thedecrease amount ΔV, it is possible to ensure sufficient precision.

In the fourth example, it is possible to calculate the internalresistance Rc without measuring the capacitance Cc of the chargeaccumulating capacitor 19. In addition, the value of the dischargecurrent may be measured only at the timing T₄. It is not necessary tomeasure the time history of the discharge current i(t).

FIFTH EXAMPLE

Next, a fifth example will be described with reference to FIGS. 7 and10. Even in the fifth example, the equivalent circuit which is shown inFIG. 7 and is the same as that of the third example is applied. In theabove-described expression (10), when t=T₅, the following expression isobtained.

[Expression  15] $\begin{matrix}{{{Vc}\left( T_{5} \right)} = {V_{0} - {\frac{1}{Cc}{\int_{0}^{T_{5}}{{i(t)}\ {\mathbb{d}t}}}} - {{Rc} \cdot {i\left( T_{5} \right)}}}} & (15)\end{matrix}$

In the same manner, when t=T₆, the following expression is obtained.

[Expression  16] $\begin{matrix}{{{Vc}\left( T_{6} \right)} = {V_{0} - {\frac{1}{Cc}{\int_{0}^{T_{6}}{{i(t)}\ {\mathbb{d}t}}}} - {{Rc} \cdot {i\left( T_{6} \right)}}}} & (16)\end{matrix}$

The following expression is obtained from the expressions (15) and (16).

[Expression  17] $\begin{matrix}{{{{Vc}\left( T_{5} \right)} - {{Vc}\left( T_{6} \right)}} = {{\frac{1}{Cc}{\int_{T_{5}}^{T_{6}}{{i(t)}\ {\mathbb{d}t}}}} - {{Rc}\left\{ {{i\left( T_{5} \right)} - {i\left( T_{6} \right)}} \right\}}}} & (17)\end{matrix}$

Since the voltage Vc(T₇) may be obtained even at the timing t=T₇ as inthe expressions (15) and (16), the following expression is obtained.

[Expression  18] $\begin{matrix}{{{{Vc}\left( T_{6} \right)} - {{Vc}\left( T_{7} \right)}} = {{\frac{1}{Cc}{\int_{T_{6}}^{T_{7}}{{i(t)}\ {\mathbb{d}t}}}} - {{Rc}\left\{ {{i\left( T_{6} \right)} - {i\left( T_{7} \right)}} \right\}}}} & (18)\end{matrix}$

In the expressions (17) and (18), the terms other than the capacitanceCc and the internal resistance Rc are physical amounts which can bemeasured as shown in FIG. 10. Accordingly, it is possible to calculatethe capacitance Cc and the internal resistance Rc by solving thesimultaneous equations with two unknowns of the expressions (17) and(18).

In the fifth example, at the timings T₅, T₆, and T₇ (T₅<T₆<T₇) aftermaking the first switch 1150N state, the capacitance Cc and the internalresistance Rc are obtained by measuring the voltage Vc(t) between theterminals of the charge accumulating capacitor 19, the discharge currenti(t), the integral value of the discharge current from the timing T₅ tothe timing T₆, and the integral value of the discharge current from thetiming T₆ to the timing T₇. Since it is not necessary to use themeasurement values of the current and the voltage abruptly changing inthe vicinity of the timing t=0, it is possible to increase the intervalwidth of the timing of measuring the voltage and the current. Inaddition, the integral value of the discharge current i(t) may becalculated in two periods among the period from the timing T₅ to thetiming T₆, the period from the timing T₅ to the timing T₇, and theperiod from the timing T₆ to the timing T₇.

In the first to fifth examples, as the hybrid type working machine, theshovel for performing the regenerating operation of the turning electricmotor 21 has been described. The method of measuring the characteristicof the charge accumulating capacitor 19 described in the examples may beapplied to the crane having a winding driving device. In this case,potential energy of the winding target is converted into electricenergy. The generated electric energy is accumulated in the chargeaccumulating capacitor 19. During the winding operation, the windingmotor is driven by the discharge current obtained from the chargeaccumulating capacitor 19 and the electric power generated from theelectric motor generator 12.

In addition, the control method of the charge accumulating circuit 90according to the above-described examples may be applied to a liftingmagnet type working machine. In this case, the suction operation of thelifting magnet is performed by the discharge current from the chargeaccumulating capacitor 19.

Since the electric motor generator 12 is rotated during the operation ofthe working machine, the voltage of the DC bus line changes due to theinfluence of the induced voltage, change in voltage being detected asnoise. In the first to fifth examples, the internal resistance or thecapacitance is measured by the charge accumulating capacitor 19 uponstarting the working machine. For this reason, it is possible to improvethe measurement precision.

In addition, in the hybrid type working machine, since the liftingoperation, the excavating operation, or the like is performed during theoperation, the charge/discharge operation of the charge accumulatingcapacitor 19 is frequently performed. For this reason, if it is notpossible to accurately understand a variation in the characteristic suchas the internal resistance of the charge accumulating capacitor 19, itis not possible to accurately calculate the charge rate. When thecalculated charge rate is not accurate, there is concern in thatsufficient power may not be supplied to the electric motor. As a result,in some cases, it is not possible to operate the working machine. In thefirst to fifth examples, it is possible to improve the calculationprecision of the capacitance and the internal resistance of the chargeaccumulating capacitor 19. Accordingly, it is possible to realize thestable operation of the working machine.

While the exemplary examples of the invention have been described, theinvention is not limited thereto. For example, it is obvious thatvarious modifications, corrections, combinations, and the like may bemade by the person skilled in the art.

1. A hybrid type working machine comprising: a first electric motorwhich performs a power running operation driven by a supply of electricpower and a regenerating operation generating electric power; a firstelectric circuit which controls the power running operation and theregenerating operation of the first electric motor; a chargeaccumulating circuit which supplies electric power to the first electricmotor and accumulates electric power regenerated by the first electricmotor; a control device which controls the first electric circuit andthe charge accumulating circuit; and a start key which activates thecontrol device, wherein the charge accumulating circuit includes: a DCbus line which is connected to the first electric circuit and in which asmoothing capacitor is connected between a ground line and a power line;a charge accumulating capacitor with an internal resistance; a converterwhich connects the DC bus line and the charge accumulating capacitor toeach other, and performs a discharge operation of supplying electricenergy from the charge accumulating capacitor to the DC bus line and acharge operation of supplying electric energy from the DC bus line tothe charge accumulating capacitor; and a first switch which performsswitching between an ON state and an OFF state, the ON state allowingcurrent to flow between the charge accumulating capacitor and the DC busline, and the OFF state not allowing current to flow between the chargeaccumulating capacitor and the DC bus line, and wherein the controldevice switches the first switch from the OFF state to the ON state dueto the start key being turned on, measures a physical quantity involvedwith a discharge characteristic of the charge accumulating capacitor,and calculates at least one of the internal resistance and a capacitanceof the charge accumulating capacitor on the basis of a measurementresult.
 2. The hybrid type working machine according to claim 1, whereinthe control device obtains a first measurement value by measuring avoltage between terminals of the charge accumulating capacitor when thefirst switch is in the OFF state, obtains a second measurement value bymeasuring a discharge current of the charge accumulating capacitor whenthe first switch is in the ON state, and calculates the internalresistance of the charge accumulating capacitor on the basis of thefirst measurement value and the second measurement value.
 3. The hybridtype working machine according to claim 2, wherein the control deviceobtains a third measurement value by measuring the discharge current ofthe charge accumulating capacitor at a time point elapsed by a firstelapsed time from a time point when the first switch becomes the ONstate, and calculates the capacitance of the charge accumulatingcapacitor on the basis of the first measurement value, the calculationvalue of the internal resistance, the third measurement value, and thefirst elapsed time.
 4. The hybrid type working machine according toclaim 2, wherein the charge accumulating circuit includes a chargingresistor which is connected in series to the charge accumulatingcapacitor, and wherein the control device calculates the internalresistance of the charge accumulating capacitor on the basis of aresistance value of the charging resistor.
 5. The hybrid type workingmachine according to claim 4, further comprising; a thermometer whichmeasures a temperature of the charging resistor, wherein the controldevice corrects the resistance value of the charging resistor on thebasis of the temperature of the charging resistor upon calculating theinternal resistance of the charge accumulating capacitor.
 6. The hybridtype working machine according to claim 1, further comprising: acharging resistor which is connected in series to the chargeaccumulating capacitor; and a second switch which is connected inparallel to the charging resistor and is configured to short-circuit thecharging resistor, wherein the control device turns on the second switchto short-circuit the charging resistor at a second timing after thefirst switch becomes the ON state, and calculates the internalresistance of the charge accumulating capacitor on the basis of avoltage between terminals of the smoothing capacitor and the chargeaccumulating capacitor immediately before the second timing and adischarge current of the charge accumulating capacitor immediatelybefore and after the second timing.
 7. The hybrid type working machineaccording to claim 6, wherein the control device calculates thecapacitance of the charge accumulating capacitor on the basis of acalculation value of the internal resistance of the charge accumulatingcapacitor and a time constant of a decrease in the discharge currentfrom the charge accumulating capacitor after turning on the secondswitch.
 8. The hybrid type working machine according to claim 1, whereinthe control device obtains a first measurement value by measuring avoltage between terminals of the charge accumulating capacitor when thefirst switch is in the OFF state, obtains a first integral value as anintegral value of a discharge current of the charge accumulatingcapacitor until a third timing elapsed by a third elapsed time from atime point at which the first switch becomes the ON state, obtains athird measurement value by measuring a voltage between the terminals ofthe charge accumulating capacitor at the third timing, and calculates acapacitance of the charge accumulating capacitor on the basis of thefirst measurement value, the first integral value, and the thirdmeasurement value.
 9. The hybrid type working machine according to claim8, wherein assuming that a capacitance of the smoothing capacitor isdenoted by Cd, a rated value of the capacitance of the chargeaccumulating capacitor is denoted by Cc, a rated value of the internalresistance is denoted by Rc, a discharge current at the third timing isdenoted by i(T₃), and the first measurement value is denoted by V₀, thethird timing is selected so that Rc×i(T₃) is equal to or less than 1/10of V₀×(Cd/(Cc+Cd)).
 10. The hybrid type working machine according toclaim 8, wherein the control device further obtains a fourth measurementvalue and a fifth measurement value by respectively measuring a voltagebetween terminals of the charge accumulating capacitor and a dischargecurrent of the charge accumulating capacitor at a fourth timing beforethe third timing and after the first switch becomes the ON state,obtains a second integral value by calculating an integral value of adischarge current of the charge accumulating capacitor until the fourthtiming from a time point at which the first switch becomes the ON state,and calculates the internal resistance of the charge accumulatingcapacitor on the basis of the first measurement value, the fourthmeasurement value, the fifth measurement value, the second integralvalue, and the calculated capacitance of the charge accumulatingcapacitor.
 11. The hybrid type working machine according to claim 1,wherein the control device obtains a first measurement value bymeasuring a voltage between terminals of the charge accumulatingcapacitor when the first switch is in the OFF state, obtains a fourthmeasurement value and a fifth measurement value by respectivelymeasuring a voltage between the terminals of the charge accumulatingcapacitor and a discharge current of the charge accumulating capacitorat a fourth timing after the first switch becomes the ON state, andcalculates the internal resistance of the charge accumulating capacitoron the basis of the first measurement value, the fourth measurementvalue, and the fifth measurement value.
 12. The hybrid type workingmachine according to claim 1, wherein the control device measures adischarge current and a voltage between terminals of the chargeaccumulating capacitor at a fifth timing, a sixth timing, and a seventhtiming elapsed by a fifth elapsed time, a sixth elapsed time, and aseventh elapsed time from a time point at which the first switch ischanged from the OFF state to the ON state, calculates integral valuesof the discharge current at two periods among a period from the fifthtiming to the sixth timing, a period from the fifth timing to theseventh timing, and a period from the sixth timing to the seventhtiming, and calculates the internal resistance and a capacitance of thecharge accumulating capacitor on the basis of the calculated integralvalues, the measured discharge current, and the measured voltage betweenthe terminals.